1. Field of the Invention
The present invention relates to a molten carbonate type or phosphate type fuel cell (referred to briefly as a "fuel cell" hereunder), a supplementary electrolyte container, and a method for supplementing the fuel cell with an electrolyte to compensate for a decrease of the electrolyte in the fuel cell during its operation.
2. Description of Related Art
When fuel cells have to be continuously operated, they are desired to be capable of operating for forty thousand hours. However, the electrolyte contained in an electrolyte member of a fuel cell gradually decreases over time due to evaporation and the corrosion of cell parts with the electrolyte. This results in an increase in internal resistance with the cell voltage being lowered. For this reason, when the cell is being operated for a long period of time, the electrolyte member must be periodically supplemented with fresh electrolyte. This supplementing is conventionally accomplished by supplying from an electrolyte storage external to the cell. In this method, however, a facility with piping necessary for the supplement must be installed externally of the fuel cell, and in addition the piping and other equipment must be made of materials resistant to corrosion by the electrolyte, which are problematic in durability and cost. A solution to these problems is described in Japanese Patent KOKAI (Laid-open) No. 60-208058. This solution employs a method consisting of filling an electrolyte-retaining matrix in a part of a gas flow path which is provided facing to an electrode on its side remote from an electrolyte-impregnated member which is sandwiched between the electrode and the other one, and allowing the electrolyte to constantly supply from the matrix to the electrolyte member owing to the capillary phenomenon. Japanese Patent KOKAI (Laid-open) No. 58-155668 discloses a method consisting of providing channels for storing an electrolyte at peripheral portions of a separator, storing an electrolyte in the channels, and supplying the electrolyte during the working time of the cell.
The electrolyte impregnated in the electrolyte member of the fuel cell is in a molten state and strongly corrosive at the cell working temperature. With respect to this point, the known methods as described above fail to take into consideration the corrosion of the electrolyte storage. That is, the stored supplementary electrolyte is in the molten state at the Working temperature of the fuel cell so that the materials constituting the electrolyte storage are gradually corroded as the cell works. The use of corrosion-resistant equipment may be considered to prevent the electrolyte storage from corrosion, but would be undesirable in view of cost. As above, the known methods fail to take into consideration the corrosion of the electrolyte storage, and cause problems as to the life and reliability of the cells.